Recently, the downsizing and performance improvement of the electric devices are under rapid development. Also, the improvement of the frequency on the transmission speed and the lowering of driving voltage are remarkable, as seen in the high-speed transmission systems such as USB 2.0, S-ATA2, HDMI or the like. On the contrary, with the downsizing or the lowering of driving voltage of the electric devices, the breakdown voltage of the electric components which are used in the electric devices is decreased. In this respect, the protection of the electric components from overvoltage becomes an important technical subject, for example, protecting the electric components against the electrostatic pulses derived from the contact between the human body and the terminal of an electric device.
In the past, in order to protect electric components from such electric pulse, a method of providing a varistor between the ground and a line to be subjected to static electricity has generally been used. As the signal frequency of the signal line is being rapidly increased in recent years, the signal quality deteriorates when the electrostatic capacitance of the ESD protection device is large. Thus, when the transmission speed is up to several hundreds of Mbps or more, a protection device with a low electrostatic capacitance (1 pF or less) is needed. In addition, an ESD protection device with a large electrostatic capacitance cannot be used in an antenna circuit and an RF module.
It has been suggested that an ESD protection device with a discharge inducing section filled between two separately and oppositely arranged electrodes can be used as an ESD device with a low electrostatic capacitance. This device is arranged between the ground and a line to be subjected to static electricity in the same way of a laminated varistor. If a much too high voltage is applied, discharge will happen between the oppositely arranged electrodes of the ESD protection device and then the static electricity will be led to the ground side. Such ESD protection device of gap type possesses properties such as a high insulation resistance, a low electrostatic capacitance and a good responsiveness.
In another respect, as an important property of the ESD protection device, the property of electrostatic adsorption is also presented as a subject of the present invention. If the discharging process occurs under a low voltage, it is necessary to restrain the peak voltage during the discharging process. If the peak voltage cannot be suppressed to a certain level, a device becoming the protection object may be destroyed. In this respect, it is necessary to restrain the peak voltage to a low level. Further, the durability issue related to repeated operations is presented here. The peak voltage should still be restrained after a plurality of discharging processes. In order to solve these technical problems, a circuit protection device, in which cavities are disposed around the oppositely arranged electrodes, is disclosed.